Real stories, please.

The whole internet is there and you are a skilled diplomat.

Convince IRL a Developer or Publisher to bring your chosen game to GOG.com and share progress/results here.

As an obvious reward, there will be a game, in our catalog, brought by you, plus your work would not go unnoticed.

Share any story starting from 2008. Thank you for your help.

Convince IRL a Developer or Publisher to bring your chosen game to GOG.com, only to be rejected by GOG.

Yeah not going to bother. One doesn't simply bring a game to GOG.

I'd much rather convince them to bring their games to itch.io, where the game won't be rejected.

Already contacted several devs on kickstarter. Mostly the answer was "GOG? Didn't really think of that". One however applied and two or three others said they would do so in the future. Edit: None of these games are finished yet.
Other devs already released on GOG, but it would be a bit exagerated to say it was my merit only.

Arthur Flabbington made it here, Randals Monday and Surviving the Humans are promised, with some luck Foolish Mortals, Bryan Scott and some others will also make it. I think also Unsung Warriors was promised after backers asked for it.

I'm sure I've suggested games here and there, but I can't recall the last time I reached out to a developer asking them to put up on GOG.
And current circumstances considering, I'm not exactly sure to do so either.

Instead of trying to convince developers, why not focus on GOG's "Submit your game" page? Convince GOG that "Use the form below to submit your game. It is around 15 questions, but we can't be bothered to count them ourselves, and we're not going to show all them from the start." isn't the way to sound like a serious business.

A few examples of the recent as well as the further past:

https://www.gog.com/forum/general/release_betrayer_available_to_play_for_free_9c440
(initiator: Tyler/tfishell)

https://www.gog.com/forum/general/breleaseb_the_dark_heart_of_uukrul_fc02e
(initiator: Scott Greig/Kill0byt3)

https://www.gog.com/forum/general/two_spicy_classics_are_ready_to_seduce_you_on_gogcom_c085f
https://www.gog.com/game/biing_sex_intrigue_and_scalpels
(initiator: a fellow German GoGlodyte who got the rights holders in contact with somebody at GoG's biz dev department, if memory serves right)